Food Biochemistry and Food Processing (2 edition)

BLBS102-c10 BLBS102-Simpson March 21, 2012 13:7 Trim: 276mm X 219mm Printer Name: Yet to Come

10 Protein Cross-linking in Food – Structure, Applications, Implications for Health and Food Safety 209

NH 3

N

H

H 2 N

NH 2

SH

HN

NH

NH

O

NH 2

OH

OH

O

O

Dehydroprotein

Disulfides

Maillard

cross-links

see figure 10.2

Uncharacterised

maillard

cross-links?

Dityrosyl

cross-links,

e.g.

+Lysine

Lysinoalanine

N

N

H

O

Glutamyl-lysine cross-links

(an isopeptide bond)

Lysine

Arginine

Histidine

Proline

Glutamine

Aspartate

(+glutamate)

Cysteine

Serine

(and derivatives)

Tyrosine

Tryptophan

Food protein,

either native

or denatured

Hydrocarbon

Largely

unreactive,

except perhaps

radical reactions?

Isopeptide bond

+Lysine

N

H

O

S

S

[O]

H

N

+other

amino acids

or Histidinoalanine,

ornithinoalanine,

+Cysteine arginine derivative

S

[O] Lanthionine

Quinone

structures,

e.g.

HO

OH

O

O

+Lysine, cysteine

proline, etc. Poorly defined

cross-link structures

Severe heat/

transglutaminase

Severe heat

Alkali Dehydroalanine

H

N

O

Alkali

Figure 10.1.A summary of the cross-linking reactions that can occur during food processing, from Gerrard 2002. Further details are given in

the text.

breakdown product (Fayle and Gerrard 2002, Friedman 1996a).

During the course of the Maillard reaction, reactive intermedi-

ates, such asα-dicarbonyl compounds and deoxysones, are gen-

erated and lead to the production of a wide range of compounds,

including polymerised brown pigments called melanoidins, fu-

ran derivatives, nitrogenous, and heterocyclic compounds (e.g.

pyrazines; Fayle and Gerrard 2002). Protein cross-links form a

subset of the many reaction products, and the cross-linking of

food proteins by the Maillard reaction during food processing

is well established (Gerrard 2002, Miller and Gerrard, in press,

2006). The precise chemical structures of these cross-links in

food, however, are less well understood. Thus, surprisingly

little is known about the extent of Maillard cross-linking in

processed foods, the impact of this process on food quality,

and how the reaction might be controlled to maximise food

quality.

In biology and medicine, where the Maillard reaction is impor-

tant during the ageing process, several cross-link structures have